Question

A supermarket selected a sample of 170 of its customers and measured how long they took to be served at the checkout counter. If too many customers wait too long, the supermarket intends to hire more checkout personnel. Specifically, the supermarket would like at least 85% of its customers to be checked out in 8.5 minutes or less. From the data, the 90^th and 60^th percentiles were computed to be 8.6 minutes and 6.7 minutes, respectively. The range of the data was 14 minutes and the fastest anyone was checked out was 1.1minutes.

What percentage of the customers were checked out between 6.7 and 8.6 minutes?

Answer 1

A supermarket selected a sample of 170 of its customers and measured how long they took to be served at the checkout counter.

From the data, the 90th and 60th percentiles were computed to be 8.6 minutes and 6.7 minutes.

Now,

8.6 minutes is the 90th percentile means 90% of the customers are checked out before 8.6 minutes.

6.7 minutes is the 60th percentile means 60% of the customers are checked out before 6.7 minutes.

So, between 6.7 and 8.6 minutes, (90-60), ie. 30% of the customers were checked out.

The answer is

30% of the customers were checked out between 6.7 and 8.6 minutes.